amstext – Typeset text fragments in mathematics

Part of the AMS-LaTeX
dis­tri­bu­tion, this pack­age de­fines a \text macro, which
makes it easy to in­cor­po­rate frag­ments of text in­side a dis­played
equa­tion or a sub or su­per­script. The font used is the
“sur­round­ing text font” and sizes are au­to­mat­i­cally
scaled in sub/su­per­scripts.